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T. Breuninger, C. Puller, S. Haverkamp, T. Euler; Chromatic Pathways in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3476.
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Color vision is wide spread among mammals, but color vision research tends to focus on primates. Studying non-primate mammals can be advantageous to understand the general principles of retinal chromatic processing. Mice, which can be easily genetically manipulated, feature like most mammals dichromatic color vision based on short (S, blue) and middle (M, green) wavelength-sensitive cone types. It is thought that mammals share a retinal circuit that compares S- and M-cone (primates: S vs. M+L) output to generate blue/green (primates: blue/yellow) antagonistic signals, with bipolar cells providing separate chromatic channels. Here, we characterized the chromatic properties of mouse bipolar cells types.
A custom-built 2P microscope was modified for dichromatic stimulation of in-vitro retina (Euler et al., 2008, Pflügers Arch, DOI 10.1007/s00424-008-0603-5). The stimulator consisted of a LCD that is alternately illuminated by LEDs (near-UV: 400BP20; green: 578BP10). Stimuli were generated by sinusoidally modulating the green and the blue components while varying their relative phase. Whole-cell recordings were carried out in slices from transgenic mice, in which different bipolar cell types were labeled.
To analyze the chromatic preference of bipolar cells we calculated the ratio of their responses to green and blue stimulus components. Responses from the same cell type tended to cluster. As expected, S cone-selective bipolar cells (Haverkamp et al., 2005, J Neurosci 25:5438-45) displayed blueON responses but also a weak greenOFF component. Among the OFF bipolar cells we found one (type 2) that showed predominantly greenOFF responses, suggesting reduced S-cone input, consistent with our immunocytochemical data. All other bipolar cell types tested responded non-selectively.
We suggest that there are at least four physiological classes of cone bipolar cells defined by their response polarity and chromatic preference: blueON, greenOFF, and non-selective ON and OFF. Our data supports the proposed antagonistically organized blue/green circuit as the common basis for dichromatic color vision in mammals.
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